1. Field of the Invention
The present invention relates generally to steam turbines, and more specifically to an apparatus and method for reducing blade "flop" that may occur during turning gear operation. The present invention has particular application to steam turbines of the type employing "axial entry, integral shroud" blades, but is not limited thereto.
2. Description of the Prior Art
Steam turbines of the type employing "axial entry, integral shroud" blades comprise a rotor with a disc (i.e., the portion of the rotor that holds the blades) having a plurality of generally fir tree-shaped, generally axially extending grooves, with the blades circularly disposed therearound. Each blade has a generally fir tree-shaped root at a proximal end thereof in registration with one of the grooves and a shroud integral with the blade at a distal end thereof. As is known, blade "flop" may occur during turning gear operation of the turbine, i.e., the blade root may rock circumferentially, and even axially, in the groove with which it is registers when the centrifugal force is insufficient to urge the root radially outward, thereby causing root/groove fretting and undesired noise. Additionally, gaps between adjacent shrouds may open under hot disc conditions and contribute to blade flop. Moreover, the mating faces of adjacent shrouds may wear from snubbing therebetween. Obviously, these are undesirable conditions.